Heat transfer label technology has been used since the early 1900's for decorating textiles and leather. In the late 1950's and early 1960's, the process was first applied to plastics. More recently, the technology has been used to provide labels on numerous surfaces, including plastic bottles.
The most common form of heat transfer label uses a wax layer as a transfer agent. In particular, the conventional heat transfer label is a multi-layered structure which incorporates a carrier or substrate, a transfer agent, inks and an adhesive layer. Optionally, a protective lacquer layer may be included as well. One such label is shown in FIG. 1. In FIG. 1, the heat transfer label 10 includes a carrier substrate 11 comprised of a supporting carrier 12 and a wax transfer agent 14, an optional protective lacquer 16, one or more inks 18, and an optional adhesive lacquer 20. Typically, the adhesive lacquer is provided, however, certain inks having a high binder content adhere well to surfaces, thereby eliminating the need for the adhesive lacquer. The supporting carrier 12 typically is a paper material, and can comprise a calendered paper or a coated paper, such as a clay coated paper. Other carrier substrates that have been used include wax-coated papers, papers coated with polymeric extrusions such as polyethylenes, polypropylenes and nylons, laminates of polyethylene or polypropylene to paper, silicone-coated papers, and polyester films having release coatings.
The transfer agent 14 is typically a layer of a material, such as wax, that melts when heated, thereby allowing the inked portion of the label to be removed from the carrier substrate 12 and adhered to a bottle or other item to be labeled. Various waxes have been used as the heat transfer agent 14. Such waxes are typically used in the form of mixtures of various waxes and typically comprise mixtures including montan waxes, victory white wax, ethylene vinyl acetate resins, paraffins, low molecular weight polyethylenes, and the like. Typically, the wax layer is approximately 2.0 to 2.5 mils in thickness. Optionally, a protective lacquer 16, is applied to the transfer agent. The protective lacquer can be any of a wide variety of known materials including polyesters, acrylics, nitrocellulose, vinylidene chloride copolymers, etc. The protective lacquer serves as a protective coating over the ink once the label has been adhered to the desired item.
Heat transfer labels of the type described above may be applied to a surface, such as the outer surface of a plastic bottle, in the manner depicted in FIG. 2. As can be seen in FIG. 2, the heat transfer label 10 formed of the supporting carrier 12, the wax transfer agent 14, the optional protective lacquer layer 16, the ink(s) 18, and the optional adhesive lacquer 20 are pressed against the outer surface of a bottle 22. More specifically, the label 10 is placed against the bottle 22 such that the adhesive lacquer 20 or the binders contained in the inks 18 are in contact with the bottle surface, while heat and pressure are simultaneously applied to the reverse (carrier substrate 11) side of the label. The elevated temperature resulting from the thermal application causes the wax forming the heat transfer agent 14 to melt and split. At the same time, the adhesive lacquer 20 and/or the binder in the inks 18 becomes tacky. The tackified label is thus caused to adhere to the bottle surface while the carrier substrate 11 is removed. The result is a carrier substrate 11 comprising a supporting carrier 12 having a thinner layer of the heat transfer agent 14 on its surface, and a bottle 22, having the heat transferred label on its surface. The adhered label will retain a portion of the heat transfer agent 14 on its exposed surface.
One problem associated with the heat transfer labels described above is a result of the heat transfer agent. Specifically, the commonly used waxes leave a thin wax layer on the label surface. This wax layer is undesirable in that it often has a residual or natural tackiness that causes it to become soiled, thereby obscuring the label and producing an unappealing product. Additionally, being relatively soft, the wax is susceptible to physical damage (i.e., scratching, scraping, etc.) that detracts from the appearance of the label and the labeled product, as well as to chemical damage that can result if the label is exposed to certain chemical agents such as caustics.
Accordingly, a need exists for a heat transfer label and labeling system that substantially eliminates the residual heat transfer agent from the label once the label has been transferred to a surface. A need also exists for heat transfer labels and labeling systems that result in a label that has a tendency to remain clean and undamaged throughout its shelf life.